JP7729052B2 - Power smoothing device, power smoothing method, and power smoothing program - Google Patents

Description

This disclosure relates to a power smoothing device, a power smoothing method, and a power smoothing program.

In recent years, the introduction of power generation equipment using renewable energy has progressed in an effort to overcome the problem of global warming and realize a carbon-free society. However, renewable energy often generates large fluctuations in power. For this reason, methods have been considered for smoothing output fluctuations in renewable energy power generation equipment by using the charging and discharging of power storage devices such as batteries. However, when calculating the target value for the combined output from the renewable energy power generation equipment and the power storage device, a phase lag (deviation) occurs with respect to the amount of power generated by the power generation equipment. In response to this, Patent Documents 1 and 2 consider methods for reducing this time lag.

Specifically, Patent Document 1 considers a method in which the solar power generated on a clear day is prepared as the standard power generation, the solar power generated by dividing the solar power generated by the standard power generation to extract the shadow fluctuation component, smoothing the shadow fluctuation component, and multiplying the smoothed shadow fluctuation component by the standard power generation to calculate the composite output target value. Furthermore, Patent Document 2 considers a method in which a second-order lag transfer function filter K(s) is applied as a method for calculating the charge/discharge power of a storage battery from the output of a power generation device.

JP 2016-140121 A Japanese Patent Application Laid-Open No. 2020-198702

However, the method described in Patent Document 1 may still cause a phase lag when smoothing the shadow fluctuation component, which may require a corresponding adjustment of charging and discharging using a power storage device. Furthermore, Patent Document 1 requires that the standard power generation be calculated in advance, making it difficult to accurately determine the power generated by solar power generation on a clear day. Specifically, when calculating the power generated by solar power generation on a clear day, various factors may affect the power generation, such as the solar panel temperature, panel deterioration or dirt, surrounding terrain (mountains and valleys), and buildings (skyscrapers, chimneys, etc.), in addition to the incident angle of sunlight, which is determined by latitude, longitude, and date and time. On the other hand, the method described in Patent Document 2 requires setting three adjustment parameters _Kp , _b1 , and _b0 as parameters for setting the renewable energy transfer function filter, but the adjustment process is not easy. In particular, depending on _b1 and _b0 , the poles of the transfer function filter K(s) may have imaginary parts, which may cause the composite output target value (or battery command) to oscillate even when the renewable energy generation power is constant. As described above, the methods described in Patent Documents 1 and 2 have room for further improvement in terms of achieving both a reduction in the capacity of the power storage device and smoothing of the output power of renewable energy.

The purpose of this disclosure is to provide technology that makes it easier to smooth the output power of renewable energy while using a small-capacity power storage device.

To achieve the above object, a power smoothing device according to one embodiment of the present disclosure is a power smoothing device that smooths the power output from a power supply system that includes a power generation device that generates power using renewable energy and a power storage device, and includes: an acquisition unit that acquires information related to the power generated by the power generation device; a calculation unit that calculates a composite output target value related to the power output from the power supply system by smoothing the generated power with reduced phase delay, and calculates the charge/discharge power from the power storage device based on the composite output target value; and an output unit that outputs an operation command specifying the charge/discharge power to the power storage device based on the calculation result of the charge/discharge power.

A power smoothing method according to one embodiment of the present disclosure is a power smoothing method for smoothing power output from a power supply system including a power generation device that generates power using renewable energy and a power storage device, and includes the steps of: acquiring information related to the power generated by the power generation device; smoothing the generated power with reduced phase delay to calculate a composite output target value related to the power output from the power supply system; calculating charge/discharge power from the power storage device based on the composite output target value; and outputting an operation command specifying the charge/discharge power to the power storage device based on the calculation result of the charge/discharge power.

A power smoothing program according to one embodiment of the present disclosure is a power smoothing program that causes a computer to smooth the power output from a power supply system that includes a power generation device that generates power using renewable energy and a power storage device. The program causes the computer to acquire information related to the power generated by the power generation device, calculate a composite output target value related to the power output from the power supply system by smoothing the generated power with reduced phase lag, calculate the charge/discharge power from the power storage device based on the composite output target value, and output an operation command specifying the charge/discharge power to the power storage device based on the calculation result of the charge/discharge power.

The above-described power smoothing device, power smoothing method, and power smoothing program calculate a composite output target value for the power output from the power supply system by smoothing the power generated by the power generation device with suppressed phase lag. Then, the charging/discharging power from the power storage device is calculated based on the composite output target value. Using this method, a composite output target value that has been smoothed with suppressed phase lag is obtained, and charging/discharging power based on this is commanded to the power storage device. Smoothing the composite output target value with suppressed phase lag reduces the difference between the composite output target value and the power generated by the power generation device, making it possible to smooth the output power of renewable energy while using a smaller-capacity power storage device. Furthermore, smoothing with suppressed phase lag can be achieved with simpler parameter adjustment than previously considered methods, making it easier to smooth the output power of renewable energy while using a smaller-capacity power storage device.

The smoothing that suppresses the phase lag may be performed by combining smoothing with phase lead compensation. By combining smoothing with phase lead compensation, the phase lag is substantially suppressed, making it possible to reduce the difference between the combined output target value and the power generated by the power generation device.

The calculation unit may further correct the calculated combined output target value based on the capacity of the power storage device to calculate the charging/discharging power from the power storage device. As described above, by further correcting the calculated combined output target value based on the capacity of the power storage device, it is possible to prevent commands from being issued to charge/discharge power under conditions that exceed the capacity of the power storage device. This makes it possible to perform control that takes the capacity of the power storage device into account.

The calculation unit may also calculate the combined output target value based on the power generation capacity of the power generation device. This configuration makes it possible to perform control that takes into account the power generation capacity of the power generation device.

The calculation unit may calculate the combined output target value so that the rate of change of the combined output target value falls within a predetermined range. When control of the rate of change of the combined output target value is required, the above configuration makes it possible to perform control that takes into account the power generation capacity of the power generation device.

This disclosure provides technology that makes it easier to smooth the output power of renewable energy while using a small-capacity power storage device.

FIG. 1 is a schematic diagram of a power supply system according to an embodiment. FIG. 2 is a diagram illustrating a conventional smoothing process. FIG. 3 is a block diagram illustrating the control unit. FIG. 4 is a diagram showing an example of fluctuations in photovoltaic power generation used in the simulation. FIG. 5 is a diagram illustrating the simulation results. FIG. 6 is a diagram illustrating the simulation results. FIG. 7 is a diagram illustrating the simulation results. FIG. 8 is a diagram illustrating the simulation results. FIG. 9 is a block diagram illustrating a control unit according to a modified example. FIG. 10 is a diagram illustrating an example of a hardware configuration of a control device.

Hereinafter, embodiments of the present disclosure will be described in detail with reference to the accompanying drawings. Note that in the description of the drawings, identical elements will be designated by the same reference numerals, and duplicate explanations will be omitted.

[Power supply system]
First, a schematic configuration of a power supply system 1 will be described with reference to Fig. 1. Fig. 1 is a schematic diagram of a power supply system according to an embodiment. The power supply system 1 includes a microgrid 2.

The microgrid 2 is connected to an external power grid 90 (external power supply grid). The microgrid 2 is capable of transmitting and receiving power to and from the external power grid 90. When the grid power is a positive value, the microgrid 2 receives power from the external power grid 90, and when the grid power is a negative value, the microgrid 2 transmits power to the external power grid 90. The microgrid 2 includes a power generation system 21 (power generation device), a power storage system 23 (power storage device), a connection unit 24, a received power measurement unit 26, a transmitted power measurement unit 27, and a control device 30 (power smoothing device).

The power generation system 21 is a system that generates power using renewable energy. In this embodiment, the power generation system 21 is a photovoltaic (PV) power generation system and includes a solar panel 21a and a power conditioning system (PCS) (not shown). The power conditioner is a power conversion device that converts the power generated by the solar panel 21a. The power conditioner converts DC power from the solar panel 21a into AC power and outputs the AC power to the connection unit 24. Note that the power generation system 21 may also be a system that generates power using renewable energy other than solar power. For example, the power generation system 21 may be a wind power generation system, a geothermal power generation system, a biomass power generation system, a waste-to-energy generation system, or other power generation system.

The power conversion capacity and AC power output capacity of the power conditioner (PCS) in the power generation system 21 are related to the power generation capacity of the power generation system 21. Therefore, the capacity of the PCS (PCS capacity) is used as an indicator of power generation capacity in the control device 30, which will be described later. Therefore, information related to the PCS capacity can also be stored in the control device 30.

The power storage system 23 is a system capable of charging and discharging power. The power storage system 23 includes a power storage device (power storage device) and a power conditioner. The power storage device may be a secondary battery such as a lithium-ion battery, a lead-acid battery, or a redox flow battery. It may also be a power storage device other than a secondary battery, such as a large-capacity capacitor, a flywheel, or a compressed air energy storage system. The power conditioner is a power conversion device that converts power between the power storage device and the connection unit 24. The power conditioner converts DC power from the power storage device to AC power and outputs the AC power to the connection unit 24. The power conditioner converts AC power from the connection unit 24 to DC power and outputs the DC power to the power storage device. The power conversion capacity and DC power output capacity of the power conditioner (PCS) in the power storage system 23 are related to the output performance from the power storage system 23. The power storage system 23 may also include a charge/discharge control device, a battery remaining capacity monitoring device, etc.

The connection unit 24 distributes power to each part, including the external power system 90. The connection unit 24 is, for example, a distribution board. The connection unit 24 has the function of notifying the control device 30 of the control content of its own device. The connection unit 24 also has the function of collecting the power generated in the power generation system 21, the charging and discharging power in the power storage system 23, and the measurement results of the received power measurement unit 26 and the transmitted power measurement unit 27. The connection unit 24 also has the function of notifying the control device 30 of this collected information from the connection unit 24.

The received power measurement unit 26 measures the power received from the external power grid 90. The transmitted power measurement unit 27 measures the power transmitted to the external power grid 90. The received power measurement unit 26 and the transmitted power measurement unit 27 are, for example, power meters.

The control device 30 acquires the operating status related to power within the microgrid 2. Furthermore, the control device 30 acquires, via the connection unit 24, the power generated by the power generation system 21, the charging and discharging power in the power storage system 23, and the measurement results of the received power measurement unit 26 and the transmitted power measurement unit 27, as described above. The control device 30 can also issue commands related to charging and discharging (charge and discharge commands) to the power storage system 23. Functionally, the control device 30 is configured to include a communication unit 31 and a control unit 32.

The communication unit 31 is, for example, a functional unit that communicates with the connection unit 24. The communication unit 31 may communicate with the connection unit 24 via a communication network, for example. The communication network may be wired or wireless. The communication unit 31 acquires information about the above-mentioned units from the connection unit 24. In other words, the communication unit 31 functions as an acquisition unit that acquires information related to the power generated by the renewable energy power generation device.

The control unit 32 is a functional unit that performs calculations for the output power of renewable energy from the microgrid 2 and transmits charge/discharge commands to the power storage system 23 based on the calculation results. In other words, the control unit 32 functions as a calculation unit that calculates the charge/discharge power in the power storage device based on the generated power, and as an output unit that outputs operation commands to the power storage device based on the calculation results by the calculation unit. The operation commands include information specifying the charge/discharge power in the power storage device. Note that the control unit 32 may be configured as a separate calculation unit and output unit.

Now, referring to Figure 2, we will explain how to smooth the output power of renewable energy. Renewable energy, such as solar power generation, is known to have large fluctuations in the power it generates depending on the time of day, weather, and season, and is sometimes referred to as variable renewable energy. Introducing a large number of renewable energy power generation systems, which have large fluctuations in power generation, could have a negative impact on the quality of the power, such as voltage or frequency. In response to this, technologies for smoothing output using power storage devices such as batteries have been studied. Generally, the target value for the combined output, which is the sum of the battery's charging and discharging power and the renewable energy power generation, is first calculated, and the output corresponding to the difference between this combined output target value and the current renewable energy power generation is adjusted using the battery.

When using this method to perform stronger smoothing, for example, operations such as increasing the time constant of the first-order lag filter or increasing the number of samples in the moving average process can be performed. However, using the above method can sometimes result in a time lag (phase lag) in the composite output target value. Figure 2 shows an example of a time lag in the composite output target value. In Figure 2, the horizontal axis represents the time of day (from 4:00 to 20:00), and the vertical axis represents power. Figure 2 also shows the power generated by solar power generation and the composite output target value smoothed using a first-order lag filter with a one-hour time constant. As shown in Figure 2, when smoothed using the above method, the composite output target value is smoother than solar power generation, but it can be seen that there is a time lag of about one hour during the rise and fall. If the composite output target value has a time lag relative to the power generated by renewable energy, the difference between the composite output target value and the power generated by renewable energy becomes larger. As a result, the charging and discharging power of the storage battery increases. Therefore, if power adjustment is to be made in line with the combined output target value, a storage battery with a larger capacity and output would be required, which could increase equipment costs.

In contrast, in the power supply system 1 according to this embodiment, the smoothing method used by the control unit 32 of the control device 30 is changed to reduce the time delay. This will be described in more detail below. In this way, the control device 30 may function as a so-called energy management system (EMS) that controls the charging and discharging power of the power storage system 23.

Instead of obtaining power information for each component from the connection unit 24, the control device 30 may obtain power information individually by connecting to the devices that make up each component individually. Furthermore, the control device 30 may be incorporated within the power storage system 23, for example.

In addition to the above-mentioned components, the microgrid 2 may also include power load devices. For example, the control device 30 in Figure 1, facility lighting devices (not shown), and EV charging stations (not shown) correspond to power load devices in the microgrid 2. However, these are not described below. This is because the power load caused by the power load devices is sufficiently small compared to the power generated in the microgrid 2 and can be ignored. Furthermore, instead of ignoring the power load caused by the power load devices, for example, fluctuations in the power generated in the power generation system 21 may be processed in a state where the power load caused by the power load devices is included.

[Control content by the control device]
Energy smoothing performed in the control unit 32 of the control device 30 will be described with reference to Fig. 3. Fig. 3 is a block diagram for energy smoothing control performed by the control device 30 shown in Fig. 1. As shown in Fig. 3, the control unit 32 is configured to include a smoothing filter 41, a phase lead filter 42, a saturator 43, and a change rate limiter 44.

The smoothing filter 41 is a filter that smooths data and is expressed, for example, by the following equation (1):

In the formula (1), _T1 is a time constant and a positive value, and s is a complex number.

The phase lead filter 42 is a filter that performs phase lead compensation and is expressed, for example, by the following equation (2):

In the formula (2), _T2 is a time constant and a positive value, and a is an adjustment parameter and a positive value.

The saturator 43 has the function of setting upper and lower limits based on the PCS capacity D1 of the power generation system 21. If the input signal is within the set upper and lower limits, the saturator 43 outputs that value; if it is below the lower limit, it outputs the lower limit value; and if it is above the upper limit, it outputs the upper limit value. The upper limit value can be set to the PCS capacity (rated capacity), for example, to prevent the combined output target value from exceeding the PCS capacity (i.e., transmitting more power than the rated solar power generation power due to discharging). The lower limit value can be set to 0 to prevent the combined output target value from becoming a negative value (i.e., receiving power due to charging). Furthermore, using the phase lead filter 42 may make the combined output target value more likely to overshoot the generated power, but applying the saturator 43 can suppress the overshoot.

The rate limiter 44 has the function of setting the rate of change of the combined output target value below a certain value. As a technical requirement for mitigating output fluctuations in the microgrid 2, the contract with the power transmission and distribution company may set clear standards for the rate of fluctuation of the combined output. In such cases, the rate limiter 44 is used to limit the rate of change so that the combined output target value does not exceed the standard. A commonly known technical requirement for mitigating output fluctuations is "less than 1% of the power plant rated output per minute." Therefore, the rate limiter 44 can be set based on the above technical requirements.

In this control unit 32, first, when the renewable energy generated power _yre is acquired, a smoothing filter 41 is applied to the renewable energy generated power _yre . Furthermore, a phase lead filter 42 is applied to the result of applying the smoothing filter 41. By applying these two filters, a calculated value of the combined output target value calculated based on the two filters is obtained. Furthermore, by applying a saturator 43 based on the PCS capacity D1 and a change rate limiter 44 to the calculated value of the combined output target value output from the phase lead filter 42, a combined output target value _rsys that takes into account the PCS capacity D1 and technical requirements related to output fluctuation mitigation is obtained.

Furthermore, by calculating the difference between the combined output target value r _sys and the renewable energy generated power y _re , a charge/discharge power command value r _bat to the power storage system 23 is calculated. If the charge/discharge power command value r _bat is positive, it indicates that the power storage system 23 needs to discharge, and if it is negative, it indicates that the power storage system 23 needs to charge.

By transmitting the charge/discharge power command value r _bat to the power storage system 23, the power storage system 23 operates with charge/discharge power y _bat according to the charge/discharge power command value r _bat . As a result, the sum of the renewable energy generated power y _re in the power generation system 21 and the charge/discharge power y _bat in the power storage system 23 becomes a composite output y _sys , which is the output power of the microgrid 2. When the composite output y _sys is positive, it indicates that power is transmitted from the microgrid 2 to the outside, and when it is negative, it indicates that the microgrid 2 receives power.

[Smoothing filters and phase lead filters]
In the above-described power supply system 1, the control unit 32 of the control device 30 combines the smoothing filter 41 and the phase lead filter 42 to determine the composite output target value, thereby performing smoothing with suppressed phase delay. This point will be described in detail.

As described above, the phase lead filter 42 is expressed by the above-mentioned mathematical formula (2). In this case, _T2 is a time constant and is a positive value. Furthermore, a is an adjustment parameter and is a positive value. As the adjustment parameter a increases, the phase lead increases. Looking at mathematical formula (2), when a=1, the denominator and numerator become equal, and F _forward (s)=1. Therefore, the adjustment parameter a is usually set to be greater than 1.

Here, smoothing can be performed more appropriately if the time constant _T2 and adjustment parameter a in the phase lead filter 42 satisfy the relationship of the following equations (3) and (4), which are set based on the time constant T1 in the smoothing filter ₄₁ as well.

In particular, when T ₂ =T ₁ and a=2, the smoothing filter 41 and the phase lead filter 42 have a special relationship. This will be explained below.

For the sake of analysis, it is assumed here that the control unit 32 does not include the saturator 43 and the change rate limiter 44. Here, the transfer function from the renewable energy generated power _yre to the battery charge/discharge power command value _rbat is defined as R(s). The transfer function R(s) is given by the following equation (5).

According to the above formula (5), it can be seen that for any a, T ₁ , T ₂ (where a > 1, T ₁ > 0, and T ₂ > 0), the poles of the transfer function R(s) (values of s where the denominator is 0, i.e., -1/T ₁ and -1/T ₂ ) have no imaginary parts. This means that even if the renewable energy generated power, which is the input signal to the transfer function R(s), undergoes a step change, the charge/discharge command to the power storage system 23, which is the output signal from the transfer function R(s), does not have any oscillatory fluctuating components. Since the command value in the charge/discharge command does not have any oscillatory fluctuating components, parameter adjustment is easier than with the method described in Patent Document 2.

When the renewable energy generated power _yre is a unit step signal, the value of the battery charge/discharge power command value _rbat at time infinity can be found from the final value theorem. In this case, it can be seen that rbat is 0 for any a, _T1 , and _T2 , as shown in the following formula (6).

The relationship shown in the above formula (6) indicates that, for any a, T ₁ , and T ₂ , if there is no change (constant) in the renewable energy generated power y _re , the charging and discharging of the storage battery is gradually stopped. In other words, this characteristic is preferable because the storage battery is installed in order to suppress fluctuations in the solar power generated.

Also, consider a case where the renewable energy generated power y _re is a ramp signal (a signal with a constant slope c [kW/s]). In this case, when the value of the storage battery command value r _bat at time infinity is calculated using the final value theorem, the relationship shown in the following formula (7) is obtained.

In the above equation (7), when aT ₂ - _{T 1} - _{T 2} = 0, the command value for the storage battery ultimately becomes 0 (when time becomes infinite). Various combinations of a, T ₁ , and T ₂ that satisfy aT ₂ - T ₁ - T ₂ = 0 are possible, but one example is the relationship T ₂ = T ₁ , a = 2. In addition to this relationship, there may be other conditions that satisfy aT ₂ - T ₁ - T ₂ = 0. However, the above relationship T ₂ = T ₁ , a = 2 can be said to be one of the simple conditions when adjusting the parameters included in both the smoothing filter 41 and the phase lead filter 42 so that aT ₂ - T ₁ - T ₂ = 0 is satisfied.

According to the above study, when the smoothing filter 41 and the phase lead filter 42 that satisfy the relation aT ₂ -T ₁ -T ₂ = 0 are selected, if the rate of change of the power generated by renewable energy is constant, the charging and discharging power of the power storage system 23 is gradually reduced. Furthermore, it can be seen that the characteristic is that the charging and discharging operation of the power storage system 23 is eventually stopped, i.e., the charging and discharging operation of the power storage system 23 is no longer performed. This corresponds to the combined output target value from the microgrid 2 gradually approaching the power generated by renewable energy, which can also be said to result in a reduced time delay. Since the capacity of the storage battery in the power storage system 23 is generally limited, controlling the charging and discharging operation of the power storage system 23 to be smaller when the rate of change of the power generated by renewable energy is constant suggests that smoothing is possible without increasing the storage battery capacity. Note that, in the case of solar power generation, a situation in which the rate of change of the power generated by renewable energy is constant can be exemplified by, for example, the rise and fall of solar power generation at sunrise or sunset. In the case of wind power generation, this can be considered as a trend component of the wind-generated power. Furthermore, even when the output control by the PCS in the power generation system 21 is changed gradually, the rate of change can be made substantially constant.

Note that under conditions where the phase lead filter 42 is not used, i.e., under conditions where only the smoothing filter 41 is used, the value of the storage battery command value r _bat at infinite time is "-T ₁ c" rather than "(aT ₂ -T ₁ -T ₂ )c" shown in the above equation (7). In other words, even if time is set to infinity, charging and discharging will continue for an amount equal to the product of the rate of change c and the time constant T _1. However, because the capacity of the storage battery is limited, it is conceivable that the storage battery will fall into a fully charged or over-discharged state over time, making it impossible to continue charging and discharging control.

It should be noted that the above considerations are based on an analysis assuming an infinite time period, and in reality, a, _{T1 ,} and _T2 do not need to be selected so as to satisfy the relational expression _aT2 - _T1 - _T2 = 0. However, if a, _T1 , and _T2 are selected so that aT2 - _T1 - _T2 is sufficiently small, it is expected that in practice, substantially the same effect as when the relational expression _aT2 - _T1 - _T2 = 0 is satisfied will be achieved. In other words, if the rate of change in power generated from renewable energy is constant, it is expected that the amount of charge and discharge by the power storage system 23 will be controlled to gradually decrease.

[Verification by simulation]
Next, a description will be given of the results of a simulation relating to the control by the control unit 32 of the control device 30. In the following simulation, a case will be described in which the power generated from renewable energy is solar power generation.

Figure 4 shows the change in the amount of solar power generated over time, which is the premise of the simulation. In this simulation, the rated output of the PCS in the solar power generation system is set to 1000 kW. Generally, the rated output of a PCS is set to 10 to 20 percent lower than the rated output of the solar panels. Therefore, as shown in Figure 4, there are cases where the maximum output remains constant during the day. In the example shown in Figure 4, it is slightly cloudy in the morning (especially between 7:00 and 10:00), and the generated power fluctuates dramatically, with a swing of about 40% of the rated output.

Meanwhile, the configuration of each part of the microgrid 2 assumed in the simulation is as follows. Specifically, the battery capacity of the power storage system 23 is 2000 kWh, the rated output is ±500 kW, and the initial capacity at the start of the simulation is 300 kWh.

The smoothing filter 41 used in the control unit 32 of the control device 30 is a first-order lag system, with a time constant _T1 of 3600 seconds. The phase lead filter 42 is set to satisfy the conditions _T2 = _T1 and a = 2. The upper and lower limits of the saturator 43 are set to 1000 kW (corresponding to the rated capacity of the PCS in the power generation system 21) and 0 kW. The fluctuation range of the change rate limiter 44 is set to ±9 kW/min. This corresponds to 0.9%/min, since the rated capacity of the PCS is 1000 kW.

On the other hand, for comparison purposes, we assumed that the smoothing device used in the conventional method would perform processing according to a block diagram that does not include the phase lead filter 42, saturator 43, and change rate limiter 44, as compared to the block diagram shown in Figure 3. Note that the functions of the storage system 23 and the time constant of the smoothing filter 41 are the same.

Using the smoothing method (proposed method) described in the above embodiment and the smoothing method (conventional method) under conditions where only the smoothing filter 41 is used for comparison, the combined output target value was calculated from the photovoltaic power generation shown in Figure 4, and further, the charge/discharge power of the storage battery, the storage battery capacity, and the combined output from the microgrid were calculated.

First, the calculation results of the combined output target value are shown in Figure 5. Figure 5 also shows the solar power generation power. Comparing the results shown in Figure 5, the proposed method using the phase lead filter 42 has a smaller phase lag with respect to the solar power generation power compared to the conventional method.

Figure 6 shows the charge/discharge power of the storage batteries in the energy storage system 23 calculated based on the composite output target value. It can be seen that the proposed method shown in this embodiment, which uses the phase lead filter 42, has a smaller maximum absolute value of the charge/discharge power compared to the conventional method, which does not use a phase lead filter. This result shows that by using a phase lead filter, control is performed to reduce the difference between the composite output target value and the amount of power generated in the power generation system 21. It can also be said that this suggests that by using the method shown in this embodiment, which uses the phase lead filter 42, it is possible to achieve smoothing of the output power even when using storage batteries with a smaller rated output.

Figure 7 shows the transition of the remaining capacity of the storage battery in the energy storage system 23. It can be seen that the proposed method using the phase-lead filter 42 in this embodiment results in less change in storage capacity than the conventional method, which does not use a phase-lead filter. This result indicates that the method using the phase-lead filter 42 in this embodiment enables smoothing with a storage battery of a smaller capacity than the conventional method. Furthermore, this method reduces the amount of energy charged and discharged by the storage battery, thereby reducing energy loss (charge and discharge loss) due to the storage battery. This means that the proposed method can increase the amount of transmitted power compared to the conventional method, thereby improving operating profits through power sales. Note that because this series of evaluations was a simulation rather than using an actual system, the storage battery capacity was set to 2000 kWh. However, this capacity is excessive compared to the rated output of a typical solar power generation system. In practice, by changing the solar power generation pattern and repeating this simulation, an appropriate storage battery capacity that is practically feasible can be calculated. Because storage battery capacity significantly affects the price of a storage battery, selecting a storage battery with an appropriate capacity can reduce initial investment costs.

Figure 8 shows the combined output from microgrid 2 (the sum of the output from photovoltaic power generation and the output from the storage battery). The proposed method shown in this embodiment, which uses the phase-lead filter 42, achieves a value that is nearly in line with the combined output target value. It also satisfies the requirement of a "fluctuation rate of 1%/minute," which can be set as a technical requirement for mitigating output fluctuations. On the other hand, with the conventional method, which does not use the phase-lead filter 42, the combined output fluctuated between 3:00 PM and 4:00 PM, and did not meet the requirement of a "fluctuation rate of 1%/minute" during this time period. This is also related to the results in Figure 6. In other words, with the conventional method, the battery's discharge power peaked at its rated power of 500 kW, making it impossible to discharge more than 500 kW. In other words, under the conditions of this simulation, the conventional method's results indicated that a stable combined output could not be achieved unless the rated output of the storage battery was increased.

[Modification]
The above-described embodiment is one embodiment of the present disclosure. The present disclosure is not necessarily limited to the above-described embodiment, and various modifications are possible without departing from the spirit of the present disclosure. Modifications will be described below.

For example, in the above embodiment, the block diagram (Figure 3) of the control unit 32 shows a configuration using the saturator 43 and the change rate limiter 44, but these may be omitted depending on the conditions of the power output from the microgrid 2. For example, if the upper and lower limits of the combined output target value do not need to be considered, the saturator 43 can be omitted. Also, for example, if the change rate of the output power does not need to be considered, the change rate limiter 44 can be omitted. In this way, the saturator 43 and the change rate limiter 44 may be omitted depending on the operational status of the microgrid 2, the characteristics of each component that makes up the microgrid 2, etc.

When arranging the smoothing filter 41, phase lead filter 42, saturator 43, and change rate limiter 44, the order may be changed. For example, the saturator 43 may be arranged after the phase lead filter 42, from the perspective of adjusting the saturator 43 so that the calculation results by the phase lead filter 42 are appropriate for the PCS capacity. On the other hand, the smoothing filter 41 may be arranged after the saturator 43 and change rate limiter 44. In this way, the arrangement can be changed depending on the function of each part.

The order of the smoothing filter 41 and the phase lead filter 42 in the block diagram of the control unit 32 (Figure 3) may also be reversed. Alternatively, the smoothing filter 41 and the phase lead filter 42 may be combined into a single filter and implemented in the control unit 32. All of these are equivalent. A Butterworth filter, Chebyshev filter, elliptic filter, or the like may also be designed and used as filters with similar characteristics to a single filter that combines a smoothing filter and a phase lead filter.

In the above embodiment, a configuration was described assuming the continuous time domain, but it may also be designed assuming the discrete time domain. In the case of the discrete time domain, the phase lead filter for the continuous time domain described above can be converted so that it can be used in the discrete time domain. Specific conversion methods include, for example, bilinear transform (also known as Tustin transform) and ZOH (Zero Order Hold) transform.

A moving average is often used as a smoothing filter in the discrete time domain, but the smoothing method is not particularly limited. For example, a weighted moving average that places weight on the most recent sample or an exponential moving average may be used. Other well-known filters, such as a low-pass FIR filter or a low-pass IIR filter, may also be used.

In the block diagram of the control unit 32 shown in Figure 3, no control (e.g., feedback control) is performed that takes into account the battery capacity. Continuing the calculations shown in Figure 3 under these circumstances could result in the battery capacity becoming inappropriate (e.g., over-discharging or over-charging), and the battery could operate abnormally. Therefore, for example, in the case of a solar power generation system, control may be added to reset the battery's SOC (State of Charge) to a target value (e.g., 100%) during sunset. In this way, when actually operating for a long period of time, various controls may be added to ensure stable operation of the power storage system (storage battery).

The control unit 32 may be configured to perform feedback of the battery capacity as needed. The block diagram shown in FIG. 9 is an example of a block diagram of a control unit 32X that performs feedback control of the battery capacity. The block diagram of the control unit 32X shown in FIG. 9 differs from the block diagram of the control unit 32 shown in FIG. 3 in the following respects. That is, an SOC target calculation unit 45 is provided downstream of the smoothing filter 41 to the change rate limiter 44. The SOC target calculation unit 45 calculates a target value of the SOC of the battery based on the calculation result by the change rate limiter 44 (the combined output target value before the battery capacity correction). The difference between the target value calculated by the SOC target calculation unit 45 and the actual SOC of the power storage system 23 (the battery) is calculated, and the result is multiplied by a proportional gain 46. This result is used as the combined output value after the battery capacity correction. The combined output value after the battery capacity correction is then again applied to a saturator 47 that sets upper and lower limits based on the PCS capacity D1 and a change rate limiter 48. This calculates the combined output target value r _sys . The flow after calculation of the combined output target value r _sys is the same as in Fig. 3. That is, a charge/discharge power command value r _bat to the power storage system 23 is calculated from the combined output target value r _sys , and based on this, the power storage system 23 operates with charge/discharge power y _bat according to the charge/discharge power command value r _bat . As a result, the sum of the renewable energy generated power y _re in the power generation system 21 and the charge/discharge power y _bat in the power storage system 23 becomes the combined output y _sys , which is the output power in the microgrid 2.

When the composite output target value r _sys is calculated based on the block diagram shown in FIG. 9 , the composite output target value can be adjusted according to the SOC of the storage battery. For example, if the current SOC of the storage battery is 90%, it is desirable to avoid further charging of the storage battery. Therefore, by setting the target SOC calculated by the SOC target calculation unit 45 to, for example, 70%, and lowering the composite output target value based on the difference from the target SOC, it is possible to prevent further charging of the storage battery (correcting it toward discharging) as much as possible. In this way, when feedback control according to the capacity of the storage battery is added, the operation described in the above embodiment can be performed using a storage battery with a smaller capacity.

In the example block diagram shown in Figure 9, as in Figure 3, the arrangement of the smoothing filter 41, phase lead filter 42, saturators 43 and 47, and change rate limiters 44 and 48 may be partially changed or omitted. As described above, appropriate changes can be made from the perspective of calculating the uncorrected combined output target value and then correcting it in accordance with the SOC of the storage battery. In this case, the saturators 43 and 47 and change rate limiters 44 and 48 may be partially omitted.

Furthermore, in the above embodiment, the power generation system 21 and the power storage system 23 are described as being connected via AC, but these parts may also be connected and controlled via DC.

In addition, while the above embodiment considers smoothing the power generation from renewable energy in a microgrid connected to an external grid, connection to an external grid is not necessarily required. For example, in isolated environments isolated from external grids, such as remote islands or rural areas, a microgrid may be configured with an unstable generator (variable renewable energy generator) that uses renewable energy such as solar power, and a stable generator such as a gas engine or diesel engine. In such cases, fluctuations in the power generated by the variable renewable energy generator must be absorbed by changing the output of the stable generator. In this case, frequent load changes in the stable generator can lead to equipment deterioration and failure. Furthermore, frequent load changes reduce combustion efficiency and increase fuel consumption. Therefore, introducing a storage battery into the microgrid can be considered to smooth the power generated by the variable renewable energy generator. The smoothing process described in the above embodiment can be suitably used in situations (equipment configurations) such as those described above.

[Hardware configuration]
The hardware configuration of the control device 30 will be described with reference to Fig. 10. Fig. 10 is a diagram showing an example of the hardware configuration of the control device 30. The control device 30 includes one or more computers 100. The computer 100 has a CPU (Central Processing Unit) 101, a main memory unit 102, an auxiliary memory unit 103, a communication control unit 104, an input device 105, and an output device 106. The control device 30 is configured by one or more computers 100 configured by this hardware and software such as a program.

When the control device 30 is composed of multiple computers 100, these computers 100 may be connected locally or via a communications network such as the Internet or an intranet. This connection logically constitutes a single control device 30.

The CPU 101 executes the operating system, application programs, etc. The main memory unit 102 is composed of ROM (Read Only Memory) and RAM (Random Access Memory). The auxiliary memory unit 103 is a storage medium composed of a hard disk, flash memory, etc. The auxiliary memory unit 103 generally stores larger amounts of data than the main memory unit 102. The communication control unit 104 is composed of a network card or a wireless communication module. At least part of the communication unit 31 may be realized by the communication control unit 104. The input device 105 is composed of a keyboard, mouse, touch panel, and microphone for voice input, etc. The output device 106 is composed of a display, printer, etc.

The auxiliary memory unit 103 stores in advance the program 110 and data necessary for processing. The program 110 causes the computer 100 to execute each functional element of the control device 30. The program 110 causes, for example, the processing related to the power adjustment method described above to be executed in the computer 100. For example, the program 110 is loaded by the CPU 101 or the main memory unit 102, and causes at least one of the CPU 101, the main memory unit 102, the auxiliary memory unit 103, the communication control unit 104, the input device 105, and the output device 106 to operate. For example, the program 110 reads and writes data from and to the main memory unit 102 and the auxiliary memory unit 103.

Program 110 may be provided in the form of a tangible storage medium such as a CD-ROM, DVD-ROM, or semiconductor memory. Program 110 may also be provided as a data signal via a communications network.

[Effect]
According to the power smoothing device (control device 30), power smoothing method, and power smoothing program described in the above embodiments, a composite output target value for the power output from the power supply system 1 is calculated by smoothing the power generated by the power generation system 21 as a power generation device with suppressed phase delay. Then, the charge/discharge power from the power storage device is calculated based on the composite output target value. By using such a method, a composite output target value smoothed with suppressed phase delay is obtained, and charge/discharge power based on the composite output target value is commanded to the power storage device. Smoothing the composite output target value with suppressed phase delay reduces the difference between the composite output target value and the power generated by the power generation device, thereby enabling smoothing of the output power of renewable energy while using a smaller-capacity power storage device. Furthermore, smoothing with suppressed phase delay can be achieved by simpler parameter adjustment than previously considered methods, making it easier to smooth the output power of renewable energy while using a smaller-capacity power storage device.

As described above, studies have been conducted in the past to smooth the power output from the power supply system 1 by setting a composite output target value in advance and correcting the phase lag when using the charging and discharging power of the power storage system 23. However, as described above, the use of small-capacity, small-output power storage devices can make adjustments difficult when smoothing the output power of renewable energy. This leaves room for further improvement in achieving both a smaller power storage device capacity and smoothing the output power of renewable energy. In contrast, the method described in the above embodiment calculates the composite output target value by smoothing with a small phase lag itself. This reduces the difference between the composite output target value and the power generated by the power generation device, thereby reducing the charging and discharging operation of the power storage device. Furthermore, smoothing with a small phase lag can be performed with simpler parameter adjustment than the method used in Patent Document 2. This makes it easier to smooth the output power of renewable energy while using a smaller-capacity power storage device.

Smoothing that suppresses phase lag may be performed by combining smoothing and phase lead compensation. As an example, a smoothing filter 41 may be combined with a phase lead filter 42. By performing smoothing in this way in combination with phase lead compensation, phase lag is effectively suppressed, making it possible to reduce the difference between the combined output target value and the power generated by the power generation device.

Furthermore, the control unit 32 as a calculation unit may further correct the calculated combined output target value based on the capacity of the power storage device to calculate the charge/discharge power from the power storage device. Specifically, for example, as shown in the example block diagram of Figure 9, a correction may be made using the difference between the target value calculated by the SOC target calculation unit 45 and the actual SOC of the power storage system 23 (storage battery). In this way, by further correcting the calculated combined output target value based on the capacity of the power storage device, it is possible to prevent commands from being issued to charge/discharge power under conditions that exceed the capacity of the power storage device. This makes it possible to perform control that takes the capacity of the power storage device into account.

The control unit 32, which functions as a calculation unit, may also calculate the combined output target value based on the power generation capacity of the power generation device. For example, by applying the saturator 43 as described above, corrections may be made that take into account the PCS capacity. With the above configuration, it is possible to perform control that takes into account the power generation capacity of the power generation device.

The control unit 32 as a calculation unit may calculate the composite output target value so that the rate of change of the composite output target value falls within a predetermined range. For example, the rate of change of the composite output target value may be adjusted by applying the change rate limiter 44 as described above. When it is necessary to control the rate of change of the power output from the power supply system 1, the above configuration makes it possible to adjust the composite output target value and adjust the output power based on this.

[Note]
The present invention demonstrates a technology that can reduce variability, a problem associated with renewable energy, at low cost, and contributes to the widespread adoption and expansion of renewable energy. Therefore, the present invention contributes to Goal 7 of the Sustainable Development Goals (SDGs) led by the United Nations, which states, "Ensure access to affordable, reliable, sustainable and modern energy for all," and Goal 13, "Take urgent action to combat climate change and its impacts."

1 Power supply system 2 Microgrid 21 Power generation system (power generation device)
23. Energy storage system (power storage device)
24 Connection unit 26 Received power measurement unit 27 Transmitted power measurement unit 30 Control device (power smoothing device)
31 Communication unit 32, 32X Control unit 41 Smoothing filter 42 Phase lead filter 43 Saturator 44 Change rate limiter 45 SOC target calculation unit 46 Proportional gain 47 Saturator 48 Change rate limiter 90 External power system

Claims (6)

A power smoothing device that smooths power output from a power supply system including a power generation device that generates power using renewable energy and a power storage device,
an acquisition unit that acquires information related to power generation by the power generation device;
a calculation unit that applies one of a smoothing filter and a phase lead filter to the generated power, and further applies the other of the smoothing filter and the phase lead filter to the result of the application, thereby calculating a composite output target value for power to be output from the power supply system, and calculates a charge/discharge power command value for the power storage device by determining a difference between the composite output target value and the generated power;
an output unit that outputs, to the power storage device , an operation command that specifies charge/discharge power according to the charge/discharge power command value based on a calculation result of the charge/discharge power command value;
A power smoothing device having: The power smoothing device of claim 1, wherein the calculation unit further corrects the calculated combined output target value based on the capacity of the power storage device to calculate the charge/discharge power from the power storage device. The power smoothing device described in claim 1 or 2, wherein the calculation unit calculates the composite output target value based also on the rated capacity of the power generation device. The power smoothing device described in any one of claims 1 to 3, wherein the calculation unit calculates the combined output target value so that the rate of change of the combined output target value falls within a predetermined range. A power smoothing method for smoothing power output from a power supply system including a power generation device that generates power using renewable energy and a power storage device, comprising:
acquiring information related to power generation by the power generation device;
applying one of a smoothing filter and a phase lead filter to the generated power, and further applying the other of the smoothing filter and the phase lead filter to the result of applying the smoothing filter to calculate a composite output target value for power to be output from the power supply system, and calculating a charge/discharge power command value for the power storage device by determining a difference between the composite output target value and the generated power;
outputting, to the power storage device , an operation command specifying charge/discharge power according to the charge/discharge power command value based on a calculation result of the charge/discharge power command value;
A power smoothing method comprising: A power smoothing program that causes a computer to smooth power output from a power supply system including a power generation device that generates power using renewable energy and a power storage device,
acquiring information related to power generation by the power generation device;
applying one of a smoothing filter and a phase lead filter to the generated power, and further applying the other of the smoothing filter and the phase lead filter to the result of applying the smoothing filter to calculate a composite output target value for power to be output from the power supply system, and calculating a charge/discharge power command value for the power storage device by determining a difference between the composite output target value and the generated power;
outputting, to the power storage device , an operation command specifying charge/discharge power according to the charge/discharge power command value based on a calculation result of the charge/discharge power command value;
A power smoothing program that causes the computer to execute the above.